Electrical relay

ABSTRACT

An electrical relay comprises: a plate-like substrate of electrically insulating material; spaced electrical contacts on one face of said substrate; a layer of selected material bridging said spaced contacts; and an electrical device provided on said substrate arranged to develop Joule heat; and in which said selected material satisfied the following criteria: (i) contains elements whose atoms when in chemical combination with other elements have an incompletely filled d-shell or an incompletely filled f-shell; (ii) contains a substance effective to remove sand p- electrons from the conduction bands of said atoms; and (iii) exhibits a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature.

United States Patent [191 Plough et al.

[ 1 ELECTRICAL RELAY [22] Filed: Sept. 29, 1972 [21] Appl. No.: 293,323

[30] Foreign Application Priority Data Oct. 1, 1971 Canada 124190 [52] US. Cl 338/23, 338/24, 317/235 Q [51] llnt. Cl H0lc 7/04 [58] Field of Search 317/235 Q; 338/225 D, 24

[56] References Cited UNITED STATES PATENTS 3,149,298 9/1964 Handelman 338/22 [111 3,843,949 1 Oct. 22, 1974 3,543,104 ll/l970 Umeda 317/235 Q 3,568,125 3/1971 Villemant et al. 317/235 Q 3,614,480 10/1971 Berglund et al. 317/235 Q 3,621,446 11/1971 Smith et al 338/23 Primary Examiner-L. T. Hix

Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher 5 7 ABSTRACT An electrical relay comprises: a plate-like substrate of electrically insulating material; spaced electrical contacts on one face of said substrate; a layer of selected material bridging said spaced contacts; and an electrical device provided on said substrate arranged to develop Joule heat; and in which said selected material satisfied the following criteria: (i) contains elements whose atoms when in chemical combination with other elements have an incompletely filled d-shell or an incompletely filled f-shell; (ii) contains a substance effective to remove sand pelectrons from the conduction bands of said atoms; and (iii) exhibits a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature.

10 Claims, 11 Drawing Figures PATENTEDumzz W974 3843949 sum 1 or 4 1 ELECTRICAL RELAY For many years relays were almost invariably electromagnetic in nature, and it was a simple matter to provide electrical isolation between the energising coil of the relay and the contacts which carried the controlled current.

However, semiconductors have opened up a' new field in switching, providing relays which are small, light, cheap and reliable to an extent difficult to achieve with any mechanical device.

In semiconductor devices, a small control current or a small control voltage is used to control a current flow. It is inherent in the principle of operation of such devices that very close spacing is used between control elements and current carried electrodes. As a result, it is not practical to use large voltages in the controlled circuit unless the circuits associated with the control elements are engineered to withstand those high voltages.

An object of the present invention is the provision of an electrical relay which, while the same order of size as a semiconductor switch or relay of similar rating, can provide virtually complete high voltage electrical isolation, for practical purposes, between its control elements and its current carrying electrodes.

According to the present invention, an electrical relay comprises: a plate-like substrate of electrically insulating material; spaced electrical contacts on one face of said substrate; a layer of selected material bridging said spaced contacts; and an electrical device provided on said substrate arranged to develop Joule heat; and in which said selected material satisfied the following criteria;

i. contains elements whose atoms when in chemical combination with other elements have an incompletely filled d-shell or an incompletely filled f-shell;

ii. contains a substance effective to remove sand p electrons from the conduction bands of said atoms; and

iii. exhibits a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature. The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a side elevation of a very small relay device, and is not drawn to scale;

FIG. 2 is a sectional upwards view taken on the line II-II of FIG. 1;

FIG. 3 is a perspective drawing of the device of FIGS. 1 and 2 mounted on a T header, the cap of which is omitted and shown in dashed outline only;

FIG. 4 is a graph showing the temperature/resistance characteristic of material used in the relay of FIGS. 1 to 3;

FIG. 5 is a perspective drawing similar to FIG. 3 and showing a modified device providing the control circuit of FIG. 9;

FIG. 6 through 9 are circuit diagrams illustrating typical uses of the device shown in FIGS. 1 to 3; and

FIGS. 10 and 11 are diagrams which illustrate the different action of this device when subjected to alternating and to direct currents.

Referring first to FIG. 1, a rectangular single crystal sapphire chip 1 having a width of 0.01 7 inch, a length of 0.030 inch and a thickness of 0.006 inch is provided, on one face only, towards its two ends with a film 3 of a nickel-chromium alloy, and on top of each film 3 is provided a gold layer 5 of smaller size than the film 3, and which serves as a terminal. The space between the two films 3 is bridged by a thin layer 4 of vanadium dioxide VO which extends up onto the film 3 but stops short of the gold layer 5.

On the reverse side of the chip 1 is provided a resistor 7 made of a nickel-chromium alloy, which acts as a heater, of the thin film type, each end of the resistor having applied to it a gold layer 8 which again serves as a terminal.

The parts so far described are mounted on a ceramic plate 9, which is shown most clearly in FIG. 3. The size of this plate is not critical except that as shown in FIG. 3 it is to be mounted in a standard T05 header 11, consisting of a metal base 13 and four contact pins l5, 17, 19 and 21 extending respectively through four insulating plugs 25, 27, 29 and 31 extending through base 13. Plate 9 is formed, in the example shown, of alumina (A1 0 Formed on the upper surface of plate 9 are four metallic contact areas 35, 37, 39 and 41 connected respectively by leads 45, 47, 49 and 51 to the the pins 15, 17, 19 and 21.

The gold layers 5 are each provided with a solder ball 53, suitably of a germanium-gold alloy or a tin-gold alloy, by which the sapphire chip 1 and the parts carried by it are. mounted on the ceramic plate 9, the two solder balls engaging respectively contact areas 35 and 37. Leads 55 and 57 respectively connect the two gold layers 8 to the two contacts areas 39 and 41.

In FIG. 3 is shown the complete assembly, a standard encapsulating top cap 59 being shown in dashed outline only.

As will be appreciated by those skilled in the art, several of the materials mentioned above in connection with the preferred embodiment can be replaced with other suitable materials, subject to a choice of materials which are compatible in the sense that the necessary sequential stages in manufacture shall not adversely affect materials and formations already established.

As regards the sapphire chip 1, alternative materials are quartz and other forms of glass, while Beryllium oxide (BeO) or alumina (A1 0 can be used. It is important that the chip be an electrical insulator of high dielectric strength, and that it has good thermal conductivity. A nickel-chromium alloy is used as a contact material since it provides a good bond to sapphire, and for other materials for the chip it may be desirable to use a different material for the film 3. The gold is used to provide a satisfactory terminal material.

The film of vanadium oxide is very important, since this material is one of a class of materials which, as they are heated through a critical temperature, suffer a very large change in resistance, of the order of l,000: l. The characteristics of this material, and of materials falling in this class, are discussed in detail below.

In the fabrication of thedevice shown in FIGS. 1 through 3, the chip 1 is first coated over its whole face with the nichrome films by an evaporation technique, known in itself, in a suitable inert atmosphere. The film typically has a thickness in the range 500 to 1000 AU (Angstrom units). The film of gold is then applied by a similar technique to a thickness of say 2,000 AU. By a photoresist process, the gold is first etched back from the central part of the chip, and then by a further photoresist process the nichrome is also etched back, but

to a slightly smaller extent, so leaving the shoulders on partial pressures of which are selected to produce the desired deposits of vanadium oxide. This film has a thickness of between 1500 and 2500 AU, and it is most important that the vanadium oxide shall be in the polycrystalline, and not in the amorphous condition. This film will cover the central part of the sapphire chip 1, the two shoulders of the nickel-chromium layer, and two contact layers of gold 5. The film is then backetched to expose the gold contact layers.

As mentioned earlier, any change in any one of the materials mentioned may require a change in the technique used, and particular care is needed toensure that no damage is caused to any of the films by excessive diffusion of the other materials which are in close proximity to it.

The material vanadium oxideis used as representative of a class of materials which suit the following definition: A body of the material:

i. contains elements whose atoms when in chemical combination with other elements have an incompletely filled d-shell or an incompletely filled f-shell;

ii. contains a substance effective to remove sand pelectrons from the conduction bands of said atoms; and

iii. exhibits a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature.

The graph of FIG. 4 shows how the resistance of a body of such a material changes as its temperature is raised and lowered through a critical temperature T In the given example, the hysteresis loop between rising temperatures and falling'temperatures is relatively wide, but it is possible by the methods used in preparing the material to obtain a narrower hysteresis loop if de- Sc SCANDIUM Ti TITANIUM V VANADIUM Cr CHROMIUM Mn MANGANESE Fe IRON Co COBALT Ni NICKEL COPPER and by many metals in the'4d seriesof elements, e.g.,

Y YTTRIUM Zr ZIRCONIUM Nb NIOBIUM Mo MOLYBDENUM Tc TECHNETIUM Ru RUTHENIUM Rh RHODIUM Pd PALLADIUM Ag SILVER and by many metals in the 5d series of elements e.g.,

Hf HAFNIUM Ta TANTALUM W TUNGSTEN Re RHENIUM Os OSMIUM Ir IRIDIUM Pt PLATINUM and by the 4 f series of elements:

La LANTHANUM Ce CERIUM Pr PRASEODYMIUM Nd NEODYMIUM Pm PROMETHIUM Sm SAMARIUM Eu EUROPIUM Gd GADOLINIUM Tb TERBIUM Dy DYSPROSIUM Ho HOLMIUM Er ERBIUM Tm THULIUM Yb YTTERBIUM Lu LUTETIUM In order to satisfy the second condition (ii), the metal can be present, as in the example given above, in the form of its oxide. Other compounds can be used, for example the nitride, the sulfate, the sulphide or the phosphide, or any other compound of the metal which will act in the specified manner, to remove the sand pelectrons from the conduction bands of the said atoms.

By way of explanation, it is pointed out that transition-se'ries elements and rare earths have incomplete dor f-shells. Therefore, where a number of atoms of such materials are placed in close proximity, an electron can move from, one dor fshell to another. If the normal valence electrons are present and uncombined (these are the sand p-electrons), the device would be useless because a strong electrical field can no longer be applied. In the device of the present invention, the valence electrons are rendered inoperative by chemical combination of the elemental metal with another element, producing, for example, a metal oxide, a metal salt or equivalent compound.

Contrary to semiconductor devices, the device of the present invention requires an element with an incomplete dor fshell. Germanium, one of the most widely used semiconductor materials, does not satisfy this requirement. 1

Many substances satisfying the first and second criteria (i) and (ii) above do not satisfy the third requirement (iii) that the material shall exhibit a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature. This property is easily ascertained for any given material by measurement of its conductivity at different temperatures. Most materials do not have a sharp change in conductivity, but exhibit a gradual change over quite a wide range of temperature.

Some of the materials which do have a sharp change in conductivity and can be used are:

Vanadium dioxide V0 Vanadium sesquioxide V 0 Silver sulphide Ag s Trititanium Pentoxide Th0,

Vanadium sesquioxide (V 0 has a sharp transition at about 150 Kelvin and a poorly defined transition at about 500 Kelvin. However, doping of this material with 1 percent of chromium sesquioxide (Cr O shifts the low temperature transition to about 170 degrees Kelvin and sharpens the high temperature transition and lowers it to about 270 Kelvin. This second transition is in the opposite direction to the first transition. This illustrates the possibility of using dopants to produce materials with useful transitions. The actual transition temperature can be adjusted by varying the amount of doping.

Considering now the operation of the device illustrated, it can be used as a relay, the state of which is changed by the heating and the cooling of the film of vanadium oxide. The vanadium oxide used in the film 4 has been doped so that its critical or switching temperature is 55 centigrade. When its temperature is below that critical temperature, the resistance between the pins 15 and 17 typically would be 200 X ohms. By applying a voltage between the pins 19 and 21, a current is caused to flow through the resistive film 7, and the heat so generated passes into the sapphire chip 1 and heats up the vanadium oxide film 4. When that film reaches its critical temperature, the resistance between pins and 17 falls abruptly to a much smaller value, typically to 200 ohms.

For example, in the specific case being described, upon dissipating power in the film 7 at a rate of 500 milliwatts, it is found that the film 4 switches after about l5 milliseconds. The time taken for the film 4 to relapse to its original low-temperature, high-resistance state (if it is carrying no current) is about the same, say 15 milliseconds. It is possible to effect more rapid switching between the high-resistance state and the low resistance state by using a higher power dissipation in film 7, but the increased heat storage in the chip causes the relapse time to be longer. It has been found possible to supply the heating power as a pulse of relatively high power, which give the desired quicker switching in the high-to-low resistance direction, while keeping down the total heat input and so enabling relatively quick relapsing to the high-resistance state.

It is convenient at this point to consider the mechanism of conduction in a film of material such as the film 4. Although, below the critical temperature, the material has a high resistance, it is still a finite resistance, and a result a small current will flow when a voltage is maintained across the material, and some ohmic heating will occur. In some circumstances, this ohmic heating on its own could be sufficient to make the material reach, locally at least, its critical temperature, and become more conductive. For most purposes, the circuit conditions will be chosen so that this does not happen at least initially, and external heating will be used to ef fect heating to the critical temperature.

As indicated by the freehand lines in FIG. 11, when the material is heated to bring it above its critical temperature, current flow is distributed over the crosssections of the material. As the current flow is reduced by external circuit conditions, or by cooling of the material to a temperature slightly less than that at which it became highly conductive, the current flow tends to become concentrated in a narrow lengthwise extending region of the material. The more concentrated current provides enough thermal heating to keep this part of the material in its more highly conductive condition.

If the applied potential is a direct-current producing potential, then a considerable reduction in either temperature or current (by external circuit action) may be needed to bring all the material down to its more highly resistive state. If the applied potential is an alternating current producing potential, then twice during each cycle the heating current and thus the heating effect will fall to zero. This permits the material to relapse into its high resistance state at a temperature usually close to the temperature at which transition in the opposite sense took place.

From the above explanation, it will be appreciated that in making use of the device it is necessary to consider whether the controlled current is alternating or unidirectional, to ascertain how the device will react to varying operating conditions.

Referring now to the circuits of FIGS. 6 through 10:

FIG. 6 illustrates a circuit which detects an overcurrent in the load R603 and turns off npn transistor O to limit the current in the load to a safe value. Resistor R605 is chosen so as to give enough base current to allow Q, to provide load current under normal operation. The film 4 is connected between the emitter and the base of transistor Q and a resistor R605 of 1000 ohms is connected between the base and collector. The heating resistor film 7 is connected in series with the load R603.

Under normal operating conditions, transistor Q is conducting since film 4 is below its critical temperature. When excess current flows through load R605 and heater film 7, the film 4 is switched to its low resistance condition and this limits the current through the load to that value which is required to maintain film 4 in the conducting state.

The circuit shown in FIG. 7 is similar to the previous one except that it is self-latching after film 4 is heated to its low resistance condition.

An npn transistor Q, is connected with the heater film 7 and a resistive load R803 across a dc. supply 805. The film is connected in series with a resistor R807 across the supply 805, and the base of the transistor is connected through Zener diode D801 to the junction of the film 4 and the resistor R807. This provides a self-latching circuit due to Joule heating in film 4 caused by the current flowing through resistor R807. The Zener diode D801 is used to bring the base of the transistor up to a correct level to offset residual voltage in film 4 when device is in the ON state. Resistor R809 is connected between the base and emitter of the transistor to shunt the leakage current of D801 away from the base of Q The circuit shown in FIG. 8 is a development of the previous circuit where an independent bias voltage supply 907 is used to offset the voltage across film 4 instead of a Zener diode. In addition, the heater film 7 is shunted with a low value resistor R905 so that the circuit can be used with higher load currents. As before,

d.c. bias supply 907 and a resistor R909 across the supply 903. The base of the transistor is connected to the junction of film 4 and resistor R909. This circuit is also self-latching after the film 4 is heated to its low resistance condition.

The circuit shown in FIG. 9 makes use of the device shown in FlGS. 1 to 3 in conjunction with a twodirection silicon controlled rectifier device 950 commonly known as a Triac. The device 950 is an a.c. switch and is connected in series with an a.c. power supply 951 and a load 953. The film 4 is connected in series with a resistor R955 of 1,000 ohms across the device 950, and the trigger electrode of the device is connected to the junction between the film 4 and the resistor R955. The heater resistor 7 is connected to a regulable control current supply 957, typically operating at voltages in the range to 50 volts. On the other hand, the voltage between the load circuit and the control circuit can well be 1,500 volts rms.

in this device, the small control voltage is used to control the resistance of the film 4, and the consequent voltage applied to the trigger electrode of the device 950 controls the current through the load 953. Current will flow in the load as long as the film 4 is maintained at above its critical temperature by the voltage applied to the heater resistor 7.

This FIG. 9 is a good illustration of the advantages of the relay device of the. present invention. The control voltage circuit is electrically isolated from the controlled. circuit, and thus it is possible to use asimple cheap and safe control circuit-to control high voltages and currents.

The circuit of FIG. 9makes use of a relay device which is comparable in size to a standard transistor, and in fact makes use of the same T05 header as illustrated in FIG. 5, but unlike such a transistor it provides electrical isolation between control and controlled circuits which is limited only by the thickness and material of the chip 1.

As mentioned above, changes can be made in the materials used, and in the configuration of the parts, while still retaining at least part of the advantages given by the invention.

The circuits shown are basic circuits, andit will be clear to those skilled in the art that temperature compensation for changes in ambient temperature can be inserted in known manner in those circuits.

We claim:

1. An electrical relay capable of providing a substantially complete high voltage isolation between its control element and its temperature sensitive switching element comprising:

a. a plate-like heat conductive supporting substrate made of electrically insulating material having a high dielectric strength and good thermal conductivity, the thickness of said substrate being approximately 0.006 inch;

b. first spaced electrical contacts on one face of said substrate;

c. a layer of selected temperature sensitive material bridging said first spaced electrical contacts;

(1. an electrical heater device providedon the opposite side of the substrate to heat said temperature sensitive material and acting as said control element; and

e. second spaced electrical contacts mounted on said electrical heater device;

f. said temperature sensitive material satisfying the following criteria:

i. contains elements whose atoms when in chemical I combination with other elements have an incompletely filled d-shell or an incompletely filled fshell;

ii. contains a substance effective to remove sand pelectrons from the conduction bands of said atoms; and

iii. exhibits a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature.

2. An electrical relay according to claim 1, in which the said electrical heater device is an electrically resistive thin film of metal.

3. An electrical relay according to claim 1, in which the selected temperature sensitive material is vanadium dioxide.

4. An electrical relay according to claim 1, in which the selected temperature sensitive material is vanadium sesquioxide.

5. An electrical relay according to claim 1, in which the selected temperature sensitive material is silver sulphide.

6. An electrical relay according to claim 1, in which the selected temperature sensitive material is trititanium pentoxide.

7. An electrical relay according to claim 2, wherein said thin film of metal is a nickel-chromium alloy and said second spaced electrical contacts are made of a layer of gold.

8. An electrical relay according to claim 1 in which the substrate is formed by a single-crystal sapphire chip and said first spaced electrical contacts are formed of a nickel-chromium alloy covered with a layer of gold.

ing both the ceramic plate and the substrate. 

1. An electrical relay capable of providing a substantially complete high voltage isolation between its control element and its temperature sensitive switching element comprising: a. a plate-liKe heat conductive supporting substrate made of electrically insulating material having a high dielectric strength and good thermal conductivity, the thickness of said substrate being approximately 0.006 inch; b. first spaced electrical contacts on one face of said substrate; c. a layer of selected temperature sensitive material bridging said first spaced electrical contacts; d. an electrical heater device provided on the opposite side of the substrate to heat said temperature sensitive material and acting as said control element; and e. second spaced electrical contacts mounted on said electrical heater device; f. said temperature sensitive material satisfying the following criteria: i. contains elements whose atoms when in chemical combination with other elements have an incompletely filled d-shell or an incompletely filled f-shell; ii. contains a substance effective to remove s- and pelectrons from the conduction bands of said atoms; and iii. exhibits a sharp change in conductivity between an insulating condition and a conducting condition at a definite critical temperature.
 2. An electrical relay according to claim 1, in which the said electrical heater device is an electrically resistive thin film of metal.
 3. An electrical relay according to claim 1, in which the selected temperature sensitive material is vanadium dioxide.
 4. An electrical relay according to claim 1, in which the selected temperature sensitive material is vanadium sesquioxide.
 5. An electrical relay according to claim 1, in which the selected temperature sensitive material is silver sulphide.
 6. An electrical relay according to claim 1, in which the selected temperature sensitive material is trititanium pentoxide.
 7. An electrical relay according to claim 2, wherein said thin film of metal is a nickel-chromium alloy and said second spaced electrical contacts are made of a layer of gold.
 8. An electrical relay according to claim 1 in which the substrate is formed by a single-crystal sapphire chip and said first spaced electrical contacts are formed of a nickel-chromium alloy covered with a layer of gold.
 9. An electrical relay according to claim 1, further comprising means for mounting said substrate on a ceramic plate of much larger size than said substrate with the layer of temperature sensitive material facing said ceramic plate but spaced therefrom, said mounting means including metallic contact areas formed on said ceramic plate and solder balls for securing said first spaced electrical contacts to said metallic contact areas.
 10. An electrical relay according to claim 9, further comprising means for mounting said ceramic plate on a header and a cap covering the header for encapsulating both the ceramic plate and the substrate. 